NEW YORK (Reuters Health) -- A common complication of prostate cancer is where the cancer metastasizes or "seeds" to bones, causing pain and an increased risk of fractures. Scientists have long searched for the reason that prostate cancer spreads to bones. A report published in the September 1st issue of Cancer Research gives a clue. The findings suggest that osteonectin, a small protein found in bone marrow, both attracts prostate cancer cells to bone and, once attracted, stimulates the cells to invade bone.

Dr. Karin Jacob, from the National Institutes of Health's National Institute of Dental and Craniofacial Research in Bethesda, Maryland, and colleagues tested the ability of various animal and human tissues, including bone, brain, liver, lung and kidney, to attract prostate cancer cells.

The investigators report that bone extracts attracted four times more prostate cancer cells than the other tissue extracts.

Further study of the bone extract revealed that the component attracting the prostate cancer cells was osteonectin, which is thought to play a role in bone mineralization. And not only did the protein "aggressively" attract cancer cells, but it also increased the ability of prostate cancer cells to invade bone, the researchers report.

The study also showed that breast cancer cells treated with osteonectin increased their production of enzymes that allow these cells to spread to bone. Breast cancer is another type of cancer that commonly spreads to bone.

The findings suggest that antibodies to osteonectin could reduce the invasiveness of prostate cancer and breast cancer cells and may offer a potential way of preventing the spread of prostate and breast cancer to bone.

"Generation of an antibody, which can specifically block prostate cancer cell metastasis to the bone, is under investigation," Jacob and colleagues write. "Such an antibody could provide a valuable tool for the treatment of prostate cancer and other bone-metastasizing cancers by blocking invasion and metastasis."